The invention relates to a light source for generating visible light, which is composed of a diode on a semiconductor basis or a semiconductor diode emitting light of a specific wavelength and of at least one luminophor into which the emitted light is directed and which luminophor generates visible light of another wavelength from the emitted light.
A light source of this type is known and is offered by Siemens AG located in Berlin and Munich under the trademark LUCO(copyright). Given this light source, the diode is composed of a light diode, which emits blue light. The luminophor generates light in the yellow spectral range by absorption of the emitted blue light. The light outputted by this light source is white light, which results from the superimposition of the light generated in the yellow spectral range and a non-absorbed portion of the emitted blue light.
The known light source has a high efficiency, is constructionally simple, has small dimensions, is inexpensive and only requires a low operating voltage enabling battery operation.
A light source for generating visible light with the aid of a diode on a semiconductor basis is also known, which is composed of three light diodes, whereby a first one only emits the primary color red, a second one only the primary color green and a third one only the primary color blue. These three diodes are arranged, for example, in a housing such that the three emitted primary colors superimpose one another and thus generate white light. A luminophor is not necessary for this light source.
This light source is also highly efficient and only requires a low electrical operating voltage enabling battery operation. The intensities of the three primary colors, however, must be exactly matched to one another. For this reason and due to the necessity of three light diodes and an involved assembly technique, this light source is more involved and expensive compared to the light source of the first cited type.
Both light sources are constructionally simple and can be realized with small dimensions compared to a traditional luminophor lamp, wherein ultraviolet light having a wavelength of 253.7 nm is emitted from a discharge in gas, and which comprises at least one luminophor into which this emitted ultraviolet light beams and which generates visible light from this emitted ultraviolet light. The gas discharge of a luminophor lamp requires high electrical voltage and the dimensions of the lamp cannot downwardly transgress specific values due to constructional reasons. Luminophor lamps reach an efficiency of approximately 20%, which is high compared to the efficiency of approximately 4% of a conventional filament lamp.
Efficiency means the ratio of the optical performance outputted by the respective light source to the electrical performance utilized for generating this performance.
Given the conventional luminophor lamp, a luminophor can be used in the form of a mixture of different luminophor substances, each of which is activated at the wavelength 253.7 nm and respectively visible light of a wavelength having a spectrum composed of a plurality of wavelengths can be generated.
The invention is based on the object of providing a light source for generating visible light, whereby a significantly greater wealth of visible wavelengths and/or spectrums are available for forming a spectrum of the generated visible light.
This object is achieved by a light source comprising at least one semiconductor diode emitting ultraviolet light and at least one luminophor which generates visible light when the ultraviolet light is directed into the luminophor.
The inventive light source is a source of the aforementioned type, whereby, in contrast to the known light source of this type, the diode does not emit visible blue light but invisible ultraviolet light and whereby the luminophor generates the visible light from the emitted ultraviolet light and not from the emitted blue light.
The visible light generated by the inventive light source is advantageously free of a superimposition of light of a color and free of light of another color from a light diode.
Given the inventive light source, the generated visible light, similar to a conventional luminophor lamp, advantageously stems from the luminophor alone, since the ultraviolet light generated by the diode is invisible.
Advantageously, every arbitrary diode generating ultraviolet light-regardless of the wavelength-can be utilized with respect to the inventive light source. A luminophor must be selected, which is activated given the ultraviolet wavelength, which is generated by the respective diode. Essentially all ultraviolet wavelengths beyond the boundary to the visible violet, particularly the wavelengths of 150 nm to 400 nm, can be advantageously generated by the currently available diodes or by the diodes that will be available at lest in the near future, so that all these wavelengths, which particularly contain the wavelength 253.7 as well, are available to the inventive light source. Separate, particularly also new luminophors, can be used for each of these ultraviolet wavelengths, so that the palette of utilizable luminophors with respect to the inventive light source is much more versatile compared to the conventional luminophor lamp.
Given the conventional luminophor lamp, the ultraviolet light is limited to the very narrow-banded wavelength range (253.7 nm) of the gas discharge. Therefore, only luminophors that are activated at the wavelength 253.7 can be used for the lamp.
In particular, a far greater number of wavelengths and/or specturms of the outputted visible light can be advantageously realized with respect to the inventive light source than before, since not only the visible wavelengths and/or spectrums of the luminophors activated at the individual ultraviolet wavelength 253.7 nm but also the visible wavelengths and/or spectrums of the luminophors activated at the ultraviolet wavelengths that are different from 253.7 are available. The additional visible wavelengths and/or spectrums generated by the additionally available luminophors can advantageously differ greatly among one another and can differ greatly from the visible wavelengths generated by the luminophors that are activated at the individual ultraviolet wavelength 253.7 nm. Given the inventive light source, a considerably greater wealth of visible wavelengths and/or visible spectrums therefore is available for the generated visible light.
Similar to the conventional luminophor lamp, a luminophor in the form of a mixture and/or laminate composed of various luminophor substances, which are activated at one and the same ultraviolet wavelength and which, at this wavelength, can generate a plurality of visible wavelengths and/or spectrums, particularly various spectrums that are situated at a plurality of visible wavelengths, for example, which are available for forming a spectrum of the visible light outputted by the inventive light source, can be advantageously used given the inventive light source.
In contrast to the conventional luminophor lamp, wherein this possibility is limited to the individual ultraviolet wavelength 253.7 nm, this possibility is advantageously given for each individual wavelength of the ultraviolet range, particularly the range of 150 nm to 400 nm, given the inventive light source. Given the inventive light source, visible wavelengths and/or various spectrums situated at visible wavelengths can be generated dependent on the utilized mixtures and/or laminates composed of various luminophor substances but also dependent on the used ultraviolet wavelength, so that the inventive light source, compared to the conventional luminophor lamp, can output visible light of a spectrum, whereby a far greater versatility of visible wavelengths and/or visible spectrums is available for forming said visible light of a spectrum.
A laminate is composed of at least two layers arranged on top of one another, which layers are to be understood as substances that are different from one another.
In comparison with the conventional luminophor lamp, a special advantage of the inventive light source is that a plurality of ultraviolet wavelengths can be used at the same time. For this purpose, the inventive light source must only have a plurality of diodes, each of which emits ultraviolet light at another wavelength, and must have at least one luminophor, which is activated at this ultraviolet wavelength, for each of these ultraviolet wavelengths.
In contrast to the conventional luminophor lamp, wherein only luminophors or luminophors in the form of a mixture composed of various luminophor substances can be utilized, which can only be activated at a specific ultraviolet wavelength, it is possible with respect to the inventive light source to use individual luminophors and/or luminophors in the form of a mixture or laminate composed of various luminophor substances, which are activated at the same time at ultraviolet wavelengths that are different from one another and which can all contribute to the formation of a spectrum of the visible light outputted by the inventive light source. In this way, the wealth of visible wavelengths and/or spectrumsxe2x80x94by means of which a spectrum of the visible light generated by the inventive light source can be composedxe2x80x94can be considerably increased once again.
A so composed visible spectrum can eclipse all visible spectrums concerning complexity and variation possibilities, which have been hitherto achieved by light sources composed of light-emitting diodes on a semiconductor basis and luminophor, and by a conventional luminophor lamp, and enables a spectrum design as desired. In particular, white light can be generated with a spectrum, which is equal to the spectrum of sunlight or which is at least very similar to it. White light, which offers a color fidelity that cannot be obtained by comparable light sources, can be generated.
Therefore, an advantageous embodiment of the inventive light source is composed of at least
a diode on semiconductor basis, which emits ultraviolet light of a wavelength,
a luminophor into which the emitted ultraviolet light of this wavelength beams and which generates visible light from this emitted light,
a diode on semiconductor basis, which emits ultraviolet light of another wavelength, which is different from the one wavelength, and
a luminophor into which the emitted ultraviolet light of the other wavelength beams and which generates visible light from this emitted light.
The luminophor activated by the ultraviolet light of a diode can basically be the same luminophor, which is activated by the ultraviolet light of the other diode, when it is a luminophor that is activated at two different wavelengths. However, it is more advantageous when a luminophor, into which ultraviolet light of a wavelength beams, differs from a luminophor into which ultraviolet light of another wavelength beams, which differs from the one wavelength.
Given a preferred embodiment of such a light source, a luminophor into which ultraviolet light of a wavelength beams, and a luminophor, which is different from this luminophor and into which ultraviolet light of another wavelength beams, which differs from the one wavelength, together form a mixture and/or laminate.
Since the ultraviolet light generated by each diode of the inventive light source is invisible, it has advantageously no color-falsifying influence on the visible light generated by the luminophor or luminophor mixture. It can be particularly avoided that white light generated by the inventive light source has a slight cast of yellow or blue dependent on the viewing angle.
A portion of the ultraviolet light generated by the diode can be advantageously simply filtered out by a plastic covering, which is impermeable for ultraviolet light, or by an assembly behind glass, which portion is not absorbed by the luminophor.
Advantageously, the inventive light source can generate white light with which objects of different color, such as lines in different colors on maps or city maps, can be better differentiated than with white light, which is generated by a known light source by superimposition of light of a color with light of another color from a light-emitting diode on a semiconductor basis.
This is based on the knowledge that white light having a line spectrum that is only composed of a few lines is disadvantageous for a differentiation of objects of different color. The last is the case, for example, when the white light is generated by superimposition of the three primary colors red, green and blue and when each of these primary colors is only composed of a narrow-banded spectral line. Objects of different color having a spectrum, which goes beyond the three narrow-banded spectral lines of the primary colors, can exhibit colors or color nuances, which are often difficult to differentiate or which can no longer be differentiated at all given illumination with white light that is only formed of the three narrow-banded spectral lines of the primary colors.
It has also been found that white light, which is formed by a superimposition of light from the yellow spectral range and which is formed by blue light, can be problematic for a differentiation of objects of different color-even though to a comparatively low degree.
The inventive light source can generate white light with one single diode, whereby objects of different color can be advantageously differentiated at least just as good with said white light as with white light generated by a conventional luminophor lamp.
In comparison with the known light source of the aforementioned type and also in comparison with the conventional luminophor lamp, the inventive light source advantageously has an efficiency that is just as high and, in comparison with the known light source, that is advantageously constructionally as simple, as small in its dimensions, as inexpensive and advantageously only requires low electrical operating voltage as well, which enables battery operation.
Given a preferred and advantageous embodiment of the inventive light source, a diode has an active layer, which emits the ultraviolet light and which is composed of a material on the basis of AlN and/or GaN. Depending on the content with respect to Al and/or Ga, all ultraviolet wavelengths, particularly the wavelengths in the range of 150 nm to 400 nm, can be basically realized by AlN and GaN and also with the aid of additives. AlxGal-xN, BxAll-xN, BxGal-xN and/or BxAly-xGayN are particularly suitable. For example, the wavelength 200 nm can be realized with pure AlN.
While AlxGal-xN is already established with respect to diodes on a semiconductor basis or a semiconductor diode emitting ultraviolet light, the boronic nitrides BxAll-xN, BxGal-xN and/or BxAly-xGal-y-xN or known given such diodes. These boronic nitrides have the advantage that they can be grown on SIC substrates in a lattice-adapted fashion. The content with respect to B should be low compared to the content with respect to Al and/or Ga. A photon energy of 5.2 eV or, respectively, 6.6 eV can be expected for BxGal-xN and BxAll-xN.
The wavelength 253.7 nm that is generated by the gas discharge of a conventional luminophor lamp and that corresponds to a photon energy of approximately 5 eV can be received given a light source comprising a semiconductor diode of an active layer selected from a group consisting of AlN, GaN, AlxGal-xN, BxAll-xN and ByAly-xGayN, when an Al-containing material, which is used for the active layer, exhibits a content of Al of at least 50%. In this case, an inventive light source can be advantageously realized, which exhibits the same luminophors composed of individual luminophor substances or mixtures composed of a plurality of luminophor substances, the same optical properties and the same high efficiency as a conventional luminophor lamp, which, however, can be advantageously significantly smaller and can be operated by battery in contrast to this lamp.
Given this realization, all luminophors as they occur in conventional luminophor lamps can be advantageously used. These luminophors are advantageously inexpensive and are available in large quantities and have been optimized toward long longevity and high efficiency. The types that are currently available advantageously even enable a specific selection of the color temperature.
Moreover, new luminophors exhibiting new luminophor substances on an individual basis or in a mixture and/or laminate can be advantageously used with respect to the inventive light source. In order to generate the visible light, the selected luminophor and a wavelength of the ultraviolet light generated by the diode must be matched to one another, regardless of whether the luminophor is conventional or new.
Every luminophor that is used in conventional luminophor lamps is optimized for ultraviolet light, which is generated by excitation of a gas discharge. Optimized generally means with regard to a luminophor that the luminophor exhibits an absorption maximum at the wavelength at which it is to be activated. In the case of the conventional luminophor lamps, each optimized luminophor exhibits an absorption maximum at the wavelength 253.7 nm.
Given the inventive light source, an increase in efficiency can be advantageously expected as a result of the utilization of new luminophors, whose absorption maximum is situated in the close ultraviolet range. This also has the advantage that diodes, which emit ultraviolet light in the close ultraviolet range, i.e., close to the wavelength 400 nm, can be currently produced particularly simple.
In order to increase the efficiency of a diode emitting ultraviolet light, it is expedient when at least a layer composed of a chemical substance is arranged in addition to the active layer of the diode, whereby said chemical substance exhibits a larger energy gap compared to the chemical substance of the active layer. Such a diode is capable of increasing the efficiency of the entire source given an inventive light source. Therefore, it is advantageous when an inventive light source has a diode, wherein at least a layer composed of a chemical substance, which has a larger energy gap compared to the chemical substance of the active layer, is arranged at the active layer.
If the material of the active layer contains Al, the layer of the larger energy gap can be realized in that the layer of the larger energy gap is composed of an Al-containing material having a higher content with respect to Al compared to the material of the active layer.
If the material of the active layer contains B, the layer of the larger energy gap can be realized in that the layer of the larger energy gap is composed of a B-containing material having a higher content with respect to B compared to the material of the active layer.
A special embodiment of the inventive light source is characterized by a diode emitting ultraviolet light at a wavelength in the range of 150 nm to 320 and by a luminophor generating visible light within this range. A particularly preferred range of the wavelength of the ultraviolet light is situated at 200 nm to 270 nm.
The inventive light source is very simple in terms of construction; advantageously exhibits long longevity in addition to high efficiency; requires only low operating voltage of a few volt and can be miniaturized. Already established technologies can be advantageously utilized for its production.
The invention is subsequently explained in greater detail on the basis of the Figures.